AQP4 and neuromyelitis optica: Although serum Abs to denatured linear AQP4 epitopes may be diagnostic for seropositive NMO (13), the uniform absence of such broad specificity to denatured epitopes in AQP4-specific rAbs derived from NMO CSF implies distinctions between global anti-AQP4 responses and the AQP4-specific B cells infiltrating the CNS.